This invention relates to a means for supplying a supply secondary air into an exhaust passage in an internal combustion engine which is provided with a turbo charger to purify the exhaust gas.
In the prior art a method has been utilized to supply secondary air into an exhaust passage in an internal combustion engine to burn the unburned components such as CO, HC or the like which are contained in the exhaust gas, thereby reducing the emission of CO or HC. In accordance with such a method, the secondary air is supplied into the exhaust passage utilizing a pressure difference between atmospheric pressure and a negative pressure (absolute pressure) which is induced by the flow of the exhaust gas in the exhaust passage. However, turbulence is created in a negative pressure pulsation generated in the high speed driving range of the engine. This makes it impossible to provide a sufficiently large pressure difference betwen the negative pressure and the atmospheric pressure. As the result, the rate of the secondary air quantity with respect to the exhausted gas quantity is decreased. In particular, since the exhaust gas pressure becomes high in the case of an internal combustion engine that is provided with a turbo charger, the rate of the secondary air quantity in the high speed driving range is lowered even more than in a conventional engine. In this case, it becomes more difficult to reduce emissions in the exhaust passage.
Conversely, if one portion of the intake air is supplied into the exhausted air passage as the secondary air supply as mentioned above, in a heavy load condition where a high output is required of the engine, for example, when ascending a slope or when accelerated abruptly, the quantity of the air which is supplied to the engine decreases, thereby making it difficult to obtain the necessary high output.